1. Field of the Invention
The present invention relates to DSRC on-vehicle device used in a road transportation system.
2. Description of the Related Art
Recently, DSRC (Dedicated Short-Range Communication) on-vehicle devices are being used in Intelligent Transport Systems (ITS) that are being developed for practical use.
Such DSRC on-vehicle device is, for example, a device used in an ETC (Electronic Toll Collection) system which makes it possible to automatically collect a toll without stopping a vehicle at a highway access or exit.
Although the DSRC on-vehicle device described above is connected to the power source of a vehicle, the vehicle power source voltage is generally either 12 V or 24 V. Therefore, DSRC on-vehicle devices must be tailored for these power source voltages, respectively. In addition, measures must be taken for preventing DSRC on-vehicle device for 12-V power source, for example, from being erroneously connected to 24-V power source.
For conventional DSRC on-vehicle devices, the following counter measures have been considered. That is, described in the user's manuals or the like that DSRC on-vehicle devices for vehicles having 12-V power source voltage should only be used to 12-V power sources, or by having the DSRC on-vehicle devices attached to vehicles only by skilled persons such as salespersons.
However, the 12-V power source sockets, mainly employed in automobiles, and the 24-V power source sockets, mainly employed in large vehicles such as a trucks are of equal size and shape. Consequently, in a DSRC on-vehicle device which receives electric power from a lighter socket, a device for 12-V power source may be erroneously connected to 24-V power source socket.
Even if the DSRC on-vehicle device is correctly connected to the 12-V power source, abnormalities such as over-voltage or low voltage may be generated by problems or the like in the battery or charger.
However, a conventional DSRC on-vehicle device does not have a device inform a user of abnormal voltage supplied from a power source. Hence, even if the power source voltage is abnormal, the user would not realize that the DSRC on-vehicle device is not correctly connected, and the DSRC on-vehicle device would not operate normally, or the DSRC on-vehicle device may be damaged by heat or the like.